Fracturing has become ubiquitous in the petroleum industry to the point that, at least in North America, almost all natural gas and the vast majority of oil wells are fractured. In fact there are more fracturing treatments than there are wells because of multiple treatments in many wells. Because of recent activities in shale gas, hydraulic fracturing of horizontal wells has become increasingly popular. However, not all reservoirs lend themselves to the same fracture and well architecture.
Other than deviated wells which we do not recommend, to match proper well architecture (vertical versus horizontal) and number and size of treatments is a very important production engineering exercise. For gas wells one of the most important additional considerations is turbulence which happens in two places: the reservoir and then in the created fracture.
This paper will discuss production from vertical, horizontal transverse and horizontal longitudinal fractured wells. Calculations of the incremental performance of each configuration are done for both oil and gas wells, using rigorous models for fractured well performance.
There are physical and economic limits and criteria. For example, for gas wells in reservoirs above 0.5 md, there is an unacceptable reduction in the performance of each transverse fracture because of enhanced turbulence effects. In such case a vertical fractured well is preferable. There are also economic criteria for selecting which type of completion is the optimum choice. Very low permeability reservoirs while attractive in North America with its controlled costs, they may be very unattractive in other countries. We look at a range of reservoir and proppant pack permeabilities and discuss the optimization of fracture geometry. The paper not only delineates areas of indicated application of each well completion but it highlights the importance of considering the hydraulic fracturing process from the very start of wellbore planning. The processes involved in planning a wellbore for efficient decision making and maximum flexibility of choice are also described.